1. Field of the Invention
The present invention relates to systems for determining the ullage of a liquid-containing tank, and relates in particular to systems of the type utilizing switches actuated by float-carried switch actuators.
2. Description of the Prior Art
The present invention is an improvement of a commercially available tank ullage determining system which utilizes a pair of tubes extending into the tank and respectively encircled by floats carrying switch actuators. Disposed in each tube is a switch connected in an electrical cable which extends upwardly through the tube and out through an opening in a stopper. When the stopper is inserted in the upper end of the tube it clamps against the cable to hold it against axial movement. A manual float lifter is provided to manually raise the floats and test the operation of the switches, which are typically respectively set at different levels corresponding, for example, to a desired high level and an overfill level. In normal operation, the floats rise and fall with the liquid level and when a float moves past a switch it actuates the switch to signal the liquid level.
In this prior system, when it is desired to change the level of a switch, the stopper is removed to free the switch cable, which can then be manually pulled up or pushed down in the tube. The difficulty with this arrangement is that there is no way to readily and accurately determine the new switch level. In order to determine this level, the manual float lifter must be used to raise the floats to actuate the switch, the distance that the float must be manually raised serving as an indication of the new switch level.